For some time, it has been desirable to accurately and consistently dispense a known volume of liquid from inside a container. Many attempts have been made to address this need.
For example, both Hester (U.S. Pat. No. 4,828,149) and Moro-Lin (U.S. Pat. No. 2,989,216) teach squeezable liquid dispensers. In each of these dispensers, a reservoir is formed in the bottom of a flexible container, and a funnel is positioned in the reservoir. The funnel is connected to a hollow tube which extends through one end of the container. When the dispensers are upright, liquid enters the funnel and flows into the tube. The liquid contained in the funnel can be dispensed when the dispensers are inverted. However, when the dispensers are upright, the height of the liquid in the tube will continue to rise until it equals the height of the liquid in the container. As a result, the volume of liquid to be dispensed depends upon the volume of liquid in the container.
In U.S. Pat. No. 2,943,767, Moro-Lin teaches another squeezable liquid dispenser. The dispenser comprises a squeezable container, and an inverted-funnel-shaped measuring cup provided inside the container. The funnel is vertically displaced from the bottom end of the container by a vertically-projecting ring, and is coupled at its upper opening to a tube which extends through the opposite end of the container. A buoyant ball is provided inside the funnel, and is free to move between the vertically-projecting ring and the upper opening of the funnel. When the container is upright, liquid contained in the container enters the funnel. As the liquid fills the funnel, the ball rises until it seals against the upper opening of the cup, whereupon further liquid flow ceases. When the container is inverted, the ball moves away from the upper opening, allowing the liquid retained in the funnel to be dispensed through the tube.
There is an apparent problem with this device, namely that the buoyant ball is free to move inside the entire volume occupied by the funnel. If the container was rotated slowly from the upright position to the inverted position, the ball could move upwards, away from the upper opening of the funnel. At the same time, liquid could still enter the funnel and flow into the tube. As a result, it appears that the device would only be effective in dispensing a controlled volume of liquid if the container was rapidly inverted.
Accordingly, there remains a need for a liquid dispensing device which can accurately and consistently dispense a pre-determined volume of liquid.